auth method schema (#131)

* Rename iam migrations to 06

* Add base tables for auth methods and auth accounts

* Add triggers for auth_method and auth_account subtypes

internal/db/migrations/postgres/04_auth.down.sql

@@ -0,0 +1,9 @@
+begin;
+
+  drop function insert_auth_account_subtype;
+  drop function insert_auth_method_subtype;
+
+  drop table auth_account cascade;
+  drop table auth_method cascade;
+
+commit;